Chromosomal rearrangements are a recently recognized genetic alteration in solid tumors including in non- small cell lung cancer (NSCLC). Rearrangements in ALK, ROS1 and RET, all of which lead to oncogenic fusion proteins, have been reported and evaluation of whether kinase inhibitors will be effect therapies for NSCLC patient harboring these genetic alterations is underway.. ALK is a validated therapeutic target based on the results of a phase III clinical trial demonstraing improved progression free survival (PFS) for ALK rearranged NSCLC patients receiving treatment with the ALK inhibitor crizotinib compared with chemotherapy. Encouraging early signs of clinical activity has also been observed for crizotinib in ROS1 rearranged NSCLC. Clinical activity of crizotinib has also been observed in ALK rearranged lymphomas and pediatric neuroblastomas. Despite the clinical efficacy of crizotinib in ALK and ROS1 rearranged NSCLC, all patients will ultimately develop acquired drug resistance. For ALK NSCLC patients,PFS is relatively short (7-8 months) suggesting that understanding the mechanisms of acquired drug resistance and developing alternative treatment strategies are urgently needed. To date, mechanisms of resistance to ALK inhibitors include secondary mutations in ALK and activation of bypass signaling pathways (mediated by EGFR or KIT). These observations have led to the preclinical and clinical development of second generation ALK inhibitors, including by us, as well therapies combining EGFR and ALK inhibitors. The understanding of the mechanisms of resistance, and strategies to overcome them, are just beginning to be understood for ALK rearranged NSCLC. For ROS1, they have not yet been described but are fully expected to occur. The co-principle investigators of this proposal have previously identified mechanisms of resistance to kinase inhibitors (including ALK targeted therapies), have developed novel non-covalent and covalent kinase inhibitors against drug resistant forms, and conducted translational and clinical studies of kinase inhibitors in NSCLC. Here we propose to integrate genomic studies of crizotinib resistant cancers from ALK and ROS1 rearranged NSCLC patients treated with crizotinib along with preclinical models of crizotinib resistance, coupled with the development of the first covalent dual ALK/ROS1 inhibitors as well as rationale combination therapies aimed at overcoming crizotinib resistance. Our findings will have direct and immediate translational relevance for ALK and ROS1 rearranged NSCLC patients. We plan to achieve these goals through the following specific aims: Aim 1: To discover and validate mechanisms of resistance to ALK targeted therapies~ Aim 2: To predict and validate drug resistance mechanism to ROS1 targeted therapies~ Aim 3: To develop the first potent and selective dual inhibitors of ALK and ROS1 with pharmacological properties suitable for testing in preclinical in vitro and in vivo models.